1. Field of the Invention
The present invention relates to an enhanced optical coupler, and in particular, to an enhanced optical coupler that is used to optically couple and align a light emitter or light detector with an optical fiber connector.
2. Background Information
Computer and communication systems are now being developed in which optical devices, such as optical fibers, are used as a conduit (also known as a wave guide) for modulated light waves to transmit information. These systems typically include a light emitter or a light detector optically connected to the optical fibers. A typical light emitter may be a so-called edge emitter, or a surface emitter, such as a vertical cavity surface emitting laser (VCSEL). A typical light detector may be a photodiode. A generic term of either a light emitter or a light detector is an xe2x80x9coptoelectronic transducer.xe2x80x9d The optical fibers, which collectively form a fiber-optic cable or ribbon, are typically coupled to the respective light detector and the light emitter, so that optical signals can be transmitted back and forth, for example.
As an example, optoelectronic transducers convert electrical signals to or from the optical signals; the optical signals carry data to a receiver (light detector) from a transmitter (light emitter) via the fiber-optic ribbon at very high speeds. Typically, the optical signals are converted into, or converted from, the associated electrical signals using known circuitry. Such optoelectronic transducers are often used in devices, such as computers, in which data must be transmitted at high rates of speed.
The conventional light emitter allows for integrated two-dimensional array configurations. For example, the active regions of a conventional VCSEL can be arranged in a linear array, for instance 12 active regions spaced about 250 microns apart, or in area arrays, for example, 16xc3x9716 arrays or 8xc3x978 arrays. Of course, other arrangements of the arrays are also possible. Nevertheless, linear arrays are typically considered to be preferable for use with optoelectronic transducers, since it is generally considered easier to align the optical fibers that collect the light emitted from the VCSELs in a linear array, than in an area array. Moreover, it is also possible to utilize the active regions singly, i.e., without being arranged in an array.
The optoelectronic transducers are normally located on either input/output cards or port cards that are connected to an input/output card. Moreover, in a computer system, for example, the input/output card (with the optoelectronic transducer attached thereto) is typically connected to a circuit board, for example a mother board. The assembly may then be positioned within a chassis, which is a frame fixed within a computer housing. The chassis serves to hold the assembly within the computer housing.
Typically, each optical fiber of the ribbon is associated with a respective active region. Further, it is conventional for the ends of the optical fibers of the ribbon to terminate in a fiber connector. Such fiber connectors usually have an industry standard configuration, such as the MTP(copyright) fiber connectors manufactured by US Conec, Ltd. of Hickory, N.C. However, fiber connectors having the industry standard configuration are not suitable for connecting directly with the sensitive active regions of the typical light emitters or light detectors. Should direct contact occur between the respective active regions and the fiber connector, the fiber connector would likely damage the active regions, causing the light emitter or light detector to become inoperative. It is thus conventional to space the fiber connector away from the active regions. However, as will be appreciated, by providing a space, it thus becomes desirable to provide a way of optically coupling the active regions with the spaced apart fiber connector, so that the optical signals can be accurately and efficiently transmitted therebetween.
One conventional manner of optically coupling the active regions with the fiber connector is to provide a lens assembly in the space therebetween. However, lens assemblies tend to be complicated and expensive. Thus, it is also known to provide a fiber optic coupler between the active regions and the fiber connector. However, the conventional fiber optic coupler has a limited length, due to manufacturing constraints. Thus, the known fiber connectors must be positioned relatively close to the active regions, which may limit design options.
Moreover, it is important to ensure that most of the light emitted from the active regions of the light emitter reaches the respective optical fibers, and that most of the light emitted from the optical fibers reaches the respective active regions of the light detector. It is thus desirable to ensure that the fiber optic coupler is precisely aligned with the respective active regions and the fiber ends disposed within the fiber connector.
It is, therefore, a principal object of this invention to provide an enhanced optical coupler.
It is another object of the invention to provide an enhanced optical coupler that solves the above mentioned problems.
These and other objects of the present invention are accomplished by the enhanced optical coupler disclosed herein.
According to one aspect of the invention, the optical coupler includes at least two plates disposed in a superposed relationship. In the exemplary aspect of the invention, the plates are essentially rectangular. Although the plates can have other shapes without departing from the spirit and scope of the invention, it is currently believed to be preferable if at least a portion of two end faces, such as opposing end faces, of the plates have a flat, planar configuration. This configuration allows the respective end faces to be brought relatively close to the active regions and fiber connector. Further, the end faces can be arranged perpendicular to a primary surface of the plates, or arranged at an angle. Moreover, one end face can be arranged perpendicularly and the other end face can be angled, for example, the end face closest to the active regions. This angled configuration may help to prevent light from being reflected back to the active regions. Moreover, since the plates are to be superposed together, it is desirable if the abutting surfaces of the plates are flat and planar. Further, the plates can mirror one another in their configuration, or have an asymmetrical configuration. For example, one of the plates may have a notch or a radius formed in the end face to accommodate wiring or other components that may be connected to the light detector/light emitter, so as to not interfere with the placement of the optical coupler.
The plates may be formed from fused silica, ceramic, or a highly filled polymer (i.e., a polymer that has a filling, such as glass), for example. These materials can be readily etched for forming the features of the optical coupler, and allow optical fibers contained within the coupler (which are separate from the optical fibers of the ribbon) to be polished without damaging the end faces of the plates. Further, such materials have similar coefficients of thermal expansion to the optical fibers, so that the various components expand and contract together. In contrast, if the plates were formed of a conventional plastic material, the material would tend to melt and coat the end faces of the optical fibers during the polishing stage. Further, plastic plates would not expand and contract with the fibers.
Moreover, the plates are preferably joined together using an adhesive, such as an epoxy resin, for example. However, the plates may be joined together using other means without departing from the spirit of the invention.
In another aspect of the invention, at least one of the plates, and preferably both of the plates have grooves formed therein. When the plates are superposed and joined together, the respective grooves of one plate face the respective grooves of the other plate to form a plurality of holes in the optical coupler, for accommodating alignment pins and optical fibers. For example, each plate can have a plurality of relatively narrow grooves extending from one side of the plate to an opposite side of the plate. Once the plates are joined together, the narrow grooves will form a plurality of through holes extending through the optical coupler. Each groove is adapted to accommodate one optical fiber therein, so that each optical fiber extends from one end of the plate to the opposite end of the plate. Moreover, each groove is sized according to the overall diameter of the optical fibers.
In another aspect of the invention, the narrow grooves are disposed parallel to each other, and are arranged in a center region of the optical coupler. Although it is believed that this configuration is preferred for use when optically coupling a fiber-optic ribbon to a light emitter or light receiver, variations in the configuration are within the scope of the invention.
In a further aspect of the invention, the optical fibers are bonded within the grooves using an adhesive, such as an epoxy. By way of example, the adhesive can be wicked down the optical fibers from a region of the end faces, after the plates are fixed together. Alternatively, the fibers and/or narrow grooves can be precoated with an adhesive prior to the placement of the optical fibers in the grooves, or the grooves and/or optical fibers can be coated with an adhesive after the optical fibers are placed in the narrow grooves, but prior to the joining of the plates.
Once the optical fibers are fixed within the optical coupler, their respective end faces can be polished to be flush with the respective end faces of the plates. The polishing, which can be performed in any known manner, causes the respective end faces to be very flat, i.e., about two microns from peak to valley. This helps in reducing any scattering of the transmitted light.
In another exemplary aspect of the invention, each plate further has a number of relatively wide grooves extending from one side of the plate to a location intermediate within the plate, for example. That is, once the plates are joined together, the wide grooves will form a plurality of wide blind holes, for example, extending into the optical coupler. Alternatively, the wide grooves can be tailored to extend across the plate, so that the wide grooves form wide through holes. Each wide groove is adapted to accommodate one alignment pin, so that a portion of the alignment pin protrudes out from the end face of the plates for connection with the fiber connector and carrier.
The wide grooves may be disposed parallel to each other, and arranged on flanking sides of the narrow grooves. Further, the wide grooves on each respective face may be spaced apart from each other by a distance that corresponds to industry standards, i.e., so that the alignment pins will be positioned to fit within receiving holes formed in the fiber connector and the carrier.
Each alignment pin may be provided with one or more annular grooves that are disposed in a region of the pin that is received within the wide grooves. The annular grooves provide a space for accommodating an adhesive, such as an epoxy, between the surface of the pins and the surface of the wide grooves. This ensures that adequate adhesive is present, despite the tight tolerance between the grooves and the pins, to secure the pins to the plates. Alternatively, or in addition to the annular grooves, the ends of the pins received within the wide grooves can be provided with a head having a diameter that is greater than a diameter of the rest of the pin. The wide groove can be tailored to have a portion having a greater thickness for accommodating the head of the respective pin, thereby securing the pin therein. Thus, the pins will be prevented from being inadvertently pulled from the grooves during insertion and removal of the optical coupler.
In a further aspect of the invention, the adhesive for fixing the pins can be injected into the respective wide holes after the plates are fixed together, or by precoating the pins with the adhesive prior to their insertion into the holes. It is also contemplated that the pins and/or grooves can be coated with the adhesive prior to the plates being fixed together.
In another exemplary aspect of the invention, each wide groove is in fluid communication with a vent groove. The vent groove extends from the respective wide groove to the outer edge of the optical coupler, and provides a passage that allows excess or expanding adhesive to vent. That is, during curing, the adhesive (such as an epoxy) may expand, causing the pins to be ejected (either partially or totally) from the respective holes. Further, the insertion of the pins into the blind holes can trap air bubbles, which can cause subsequent epoxy blow-out through the hole, and contamination of the end face surfaces of the optical coupler. In either scenario, the optical coupler may be prevented from performing an adequate job of coupling. The vent grooves provide a means of relieving any pressure buildup within the blind holes, thus preventing the above problems. Moreover, although some of the adhesive may be expelled through the vents, it can be directed to an area of the optical coupler where it will not cause damage or undesirable contamination. Further, any adhesive that does end up in the vents will assist in adhering the plates together, by forming a mechanical lock.
In another aspect of the invention, the wide holes are chamfered at their openings. This reduces any sharp edges that may be otherwise located at the openings, and which would otherwise be subject to chipping and cracking during the insertion of the pins within the respective holes.
In a further aspect of the invention, the various grooves may have a v-shaped or other geometrical configuration. A v-shaped configuration may be the easiest configuration to make, from a manufacturing standpoint. Alternatively, each of the grooves may be provided with xc2xd of a hexagonal configuration, so that once the plates are joined together, the respective holes have a hexagonal shape. Such a shape may be more advantageous for supporting the pins or optical fibers, since such a shape will provide for more supporting surfaces that a v-shaped groove. Moreover, the hexagonal shape will more closely match the shape of the optical fibers, thus reducing voids therebetween that may entrap air and reduce the strength of the bond.
The various grooves may be formed by etching in any conventional manner. For example, the grooves could be etched using known chemical etching techniques or by using lasers. Etching is preferred to other manufacturing techniques, such as molding, since molds tend to degrade overtime. Thus, an optical coupler formed in a mold will not be as accurately formed in an older mold as in a newer mold. In contrast, optical couplers formed using etching techniques will be formed in a consistent manner throughout the manufacturing process. Further, it is difficult to precisely form an optical coupler using molding techniques. For example, in a molded optical coupler, the holes for the optical fibers would tend to be relatively short, for example xc2xc inch, since holes of a greater length can not be accurately made in an economical manner. In contrast, an optical coupler manufactured using etching techniques is not limited in size, since the holes are first formed as grooves, which can be made to be any desired length. Moreover, although it is currently believed that etching provides for the most accurate formation of the grooves, the grooves may also be formed using other machining techniques, such as by dicing or grinding.
In use, the prepared optical coupler is joined to the fiber connector by inserting the appropriate pins of the optical coupler into associated holes formed in the fiber connector. The optical coupler is also joined to the carrier of the light emitter/light detector in a similar manner. For example, the carrier may have the light emitter attached thereto, and may be provided with lands that project beyond the light emitter. The lands could be provided with holes that receive the appropriate pins of the optical coupler. In this manner, the optical coupler can be spaced apart from the active regions, for example by a few microns, so as to not directly contact the active regions. Further, the respective pins could be fit into the respective holes using a clearance fit, so that the optical coupler could be actively aligned with the light emitter, for example, in a manner well known to those skilled in the art.